1. Field of the Invention
The present invention relates to a viscous fluid type heat generator which includes a housing provided with a heat generating chamber and a heat receiving chamber separated from each other, and a rotor element for shearing a viscous fluid contained in the heat generating chamber to generate heat that is in turn transmitted to a heat exchanging fluid circulating through the heat receiving chamber to be carried by the heat exchanging fluid to a desired area to be heated.
2. Description of the Related Art
A viscous fluid type heat generator which may be incorporated in a vehicle heating system is known in the art, and one example is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 8-337110 (JP-A-8-337110). In this viscous fluid type heat generator, a housing assembly defines therein a heat generating chamber and a heat receiving chamber arranged adjacent to the heat generating chamber. The heat generating chamber is isolated from the heat receiving chamber by a partition wall through which heat is exchanged between a viscous fluid accommodated in the heat generating chamber and a heat exchanging fluid flowing through the heat receiving chamber. The heat exchanging fluid is introduced through an inlet port into the heat receiving chamber, and is delivered through an outlet port from the heat receiving chamber to an external heating circuit.
A drive shaft is supported for rotation by a bearing unit in the housing assembly and sealed by a sealing device therein. A rotor element, which may be made of a plastic material, is fixedly mounted on the drive shaft at the rear end thereof in such a manner as to be able to rotate within the heat generating chamber. An electromagnetic clutch is provided on the drive shaft at the front end thereof to transmit the output torque of a vehicle engine to the drive shaft through the clutch. The rotor element includes outer surfaces arranged face-to-face with the inner wall surfaces of the heat generating chamber to define therebetween a fluid-tight gap. The viscous fluid is supplied into the heat generating chamber to be held in the fluid-tight gap.
When the output torque of the vehicle engine is transmitted through the electromagnetic clutch to the drive shaft to rotationally drive the drive shaft, the rotor element is also rotated within the heat generating chamber. At this time, the rotating rotor element applies a shearing stress to the viscous fluid held in the gap between the inner wall surfaces of the heat generating chamber and the outer surfaces of the rotor element, and thereby the viscous fluid generates heat. The generated heat is then transmitted from the viscous fluid to the heat exchanging fluid circulating through the heat receiving chamber, and the heat exchanging fluid carries the transmitted heat to the heating circuit of the vehicle heating system to heat a passenger compartment.
In the conventional viscous fluid type heat generators, it is generally difficult to ensure both the large amount of heat generation and the durability of the components of the generator.
That is, to ensure the large amount of heat generation in this type of heat generator, it is desired that the fluid-tight gap between the inner wall surfaces of the heat generating chamber and the outer surfaces of the rotor element is small. However, when the rotor element continuously rotates after it starts for rotation, the temperature of the viscous fluid rises to a high level due to the heat generation thereof, and thereby, parts of the housing assembly, which constitute the walls of the heat generating chamber, as well as the rotor element expand due to the temperature rise, to a significant extent.
Consequently, there are some cases where the dimension of the fluid-tight gap is further reduced, though the cases depend on the selection of materials of the chamber wall parts of the housing assembly and the rotor element, and where the reduced gap causes an interference or a frictional sliding between the chamber wall part and the rotor element. Also, in such cases, even if the passenger compartment has been sufficiently or satisfactorily heated, the viscous fluid continuously and increasingly generates heat, which may result in heat and/or mechanical deterioration of the components of the heat generator.
Particularly, when the conventional heat generator, as described in JP-A-8-337110, includes a plastic rotor element and a metal housing assembly, in consideration of the heat resistance of the housing assembly, the durability of the components of the generator may be deteriorated because the thermal expansion coefficient of plastic material is normally larger than that of metal. Further, when this heat generator is incorporated in the vehicle heating system, the vehicle engine frequently drives the drive shaft at a high speed of rotation, e.g., thousands of r.p.m., and thereby the viscous fluid may generate heat at a temperature of several hundreds of degrees (.degree. C.). Consequently, if the rotor element is made of plastic materials, the rotor element in itself tends to have low heat resistance.